Certain natural fibers benefit digestive function, help prevent intestinal and colon cancer and act as fecal gastroenteral bulking agents. Generally, fibers are derived from grains, and are composed of polysaccharides with a range of structures. The role of fiber in health has become well recognized; however, its mechanisms of action are not completely understood.
Yeast cell walls are largely made up of the hydrophilic polysaccharide beta-glucan. The cell wall is primarily composed of a .beta.(1-3)-linked glucose polymer with periodic .beta.(1-6)-linked side chains. A similar polysaccharide can be found in grains, such as barley, which are common sources of dietary fiber.
The term "fiber" refers generally to a diverse, complex group of substances whose single common attribute is their resistance to human digestive enzymes. The important physiological effects of fiber are related to this characteristic, as well as to water and ion-binding capacity, viscosity, and the products of their fermentation in the bowel. E. Bright-See, Nutrition Today, 4:4-10 (1988). The implication is that fiber increases bulk, dilutes colonic contents, speeds transit time and changes bacterial metabolism, possibly providing protection from some diseases of the gut. Furthermore, diets high in fiber are usually lower in animal products, (i.e., saturated fat, cholesterol). By replacing or reducing these fats, protection against heart disease is enhanced. P. M. Kris-Etherton et al., Journal of the American Dietetics Association, 88:1373-1400 (1988); S. Bingham, American Journal of Clinical Nutrition, 45:1226-1231 (1987). Dietary fiber can alter lipid metabolism by interfering with cholesterol absorption, changing lipoprotein lipase activity or fatty acid metabolism. Also, fiber has been seen to lower blood glucose levels, alter hormonal levels and influence carbohydrate metabolism. Epidemiological evidence does suggest a link between reduced incidence of chronic heart disease and colon cancer in populations consuming high fiber diets. T. A. Miettinen, American Journal of Clinical Nutrition, 45:1226-1231 (1987); M. L. Wahlevist, American Journal of Clinical Nutrition, 45:1232-1236 (1987). Most authorities agree that dietary fiber intake should be increased from the current average of 10-20 gm/day to 25-30 gm/day, but not to exceed 45 gm/day. For most, this can be safely accomplished by consuming a variety of foods containing fiber.
It is known that a diet high in fiber is beneficial for a variety of reasons. Dietary fiber aids digestion because it provides an indigestible biomass which is carried through the alimentary canal causing undigested food to be pushed out before it. Fiber also clears out bacteria and insures the proper working of the peristaltic muscles. A diet high in fiber has been shown to reduce serum cholesterol and triglyceride levels, and has been linked to lower rates of intestinal and colon cancer. A high fiber diet has also been linked to the reduction of other problems commonly associated with poor digestion, such as ulcer formation, ileitis and colitis.
Dietary fiber is particularly important for persons on a liquid diet, such as, for example, a patient who receives nourishment through a feeding tube due to inadequate function of the gastro-intestinal tract, with or without protein calorie malnutrition. A common side effect for those patients who do not receive any fiber supplement is chronic diarrhea due to lack of bulk. This condition may cause depletion of essential nutrients in the patient, dehydration and bowel irritation. Some dietary fibers can be used as a stool or fecal bulking agent to aid digestion and control chronic diarrhea. A fiber having a large water holding capacity is useful for this purpose, because these fibers absorb excess fluid in the colon resulting in increased fecal wet weight and stool number. Furthermore, some fibers are partially digested by bacteria in the large bowel, forming short chain fatty acids, which are preferred energy fuels for the small intestine and improve intestinal function.
Grain .beta.-glucans are commonly used as a source of fiber. Another source of .beta.-glucans is yeast cell walls; however, yeast .beta.-glucans have not been used as a dietary fiber supplement due to the fact that yeast cell wall glucans prepared by traditional methods, such as the method described by Manners et al. , in Biochem. Journal, 135:19-30 (1973), are not pure, and generally contain materials such as protein, glycogen and chitin. Also, the water-holding capacity of .beta.-glucans prepared previously is low due to the presence of hydrophobic components such as protein and glycogen, and due to the lack of any three-dimensional cell wall micro-structure. Functionality and purity of a compound to be used for non-irritating, food-grade, fiber preparations are essential to ensure acceptable performance and qualitative properties, such as bland taste and white coloration.